A Hierarchical Objective Set Covering Model for Emergency Medical Service Vehicle Deployment

The use of hierarchical and multiobjective programming in public decision making is reviewed. The conventional set covering (CSC) problem is formulated for locating emergency medical service (EMS) vehicles. Its computational and practical limitations are discussed. The desire to account for inter-district responses leads to the formulation of a hierarchical objective set covering (HOSC) problem in which we find the minimum number of vehicles needed to cover all zones while simultaneously maximizing the extent of multiple coverage of zones. Several important properties of the HOSC problem are derived, including the fact that for certain values of the relative weights associated with the two objectives, no dominated zones are included in the solution. The CSC and HOSC formulations are applied to a 33-zone problem for Austin, Texas, and computational experiences are indicated.